ata: sata_rcar: make sata_rcar_ata_devchk() return 'bool'

sata_rcar_ata_devchk() returns 1 if a device is present, 0 if not --
the 'bool' type clearly fits better here than 'unsigned int'...

Signed-off-by: Sergey Shtylyov <s.shtylyov@omp.ru>
Signed-off-by: Damien Le Moal <damien.lemoal@opensource.wdc.com>